Air heating furnace



April 14, 1942. A. A. oLsoN AIR HEATING FURNACE.

Filed March 26, 1940 2 Sheets-Sheet l wvam/boo ARTHUR A. OLSON April 14, 1942. A. A. oLsoN AIR HEATING FURNACE Filed March-2e, 1940 2 Sheets-Sheet 2 l f, Ira

lwuem/bo'v ARTHUR A. oLsoN ber also at high temperatures.

Patented Apr. 14, 1942 UNITED STATES PATENT OFFICE AIR HEATING FURNACE Arthur A. Olson, Youngstown, Ohio I Application March 26, 1940, Serial No. 326,017

2 Claims.

This inventionrelates to an air heating furnacel and more particularly to an air heatingfurnace of the kind in which the air to be heated is moved at high velocity through a plurality of air conducting tubes having high heat conducting walls and positioned in a furnace employing substantially high temperatures. More specifically, the invention relates to an air heating furnaceof the kind disclosed in United States Patent 1,488,011 to Leif Lee and is an improvement thereover.

The air heating furnace of the kind involved consists of a combustion chamber, an outwardly extending flue, a heating chamber coextensive with the flue and communicating with the end of the flue opposite the combustion chamber, exhaust ports for the heating chamber in the end thereof adjacent the combustion chamber and a plurality of heat transferring, air conducting tubes positioned in the heating chamber; The

flue and the heating chamber are separated by a refractory wall and in practice this wall forms the roof of the heating chamber with the flue being provided between this wall and the roof of the furnace proper. economy of construction is effected by supporting the refractory tiles constituting the partition di- Simplicity of design and all the air heating tubes employed will be subrectly on the air conducting tubes which for` lvarious reasons are arch shaped.

In the construction of furnaces of the kind described it has been the usual practice to arrange the heating chamber as extending horizontally outward from the combustion chamber with the flue superimposed thereover. Since combustion continues and is completed in the flue, high tem- I peratures are developed therein and the gaseous products of combustion enter the heating cham- In the modification specifically disclosed in the above mentioned patent the air heating tubes in the heating chamber are shown as being arranged transversely to the longitudinal path of travel of the heating gases through the heating chamber and it was found in practice that those tubes which are adjacent the opening between the ue and the heating chamber were subjected to much higher temperatures than the tubes positioned toward the other end of the heating chamber and would be burnt out long before the other tubes of the furnace were deteriorated. In an attempt to overcome this operating difficulty the tubes were arranged in planes parallel with the direction of flow of the gaseous products of combustion through the heating chamber and, since all the tubes were now subjected to a more equal temjected to substantially thev same temperatures, thus reducing the probability ofearly failure of.

any of the tubes.

Another object of the invention is the increasing of the eiciency of the operation4 of a furnace of the kind described and this is accomplished in accordance with the invention by increasing substantially the recuperative effect of the furnace.

In accordance with the invention the total amount of air passing througheach of the independent tubes is proportioned in relation to the length of the tube and to the temperatures to which the tubes are subjected, thus a greater total volume of air is passed through the longer outer tubes whichare also subjected to the high- "C est temperatures and a lower total volume of air is passed through the shorter inner tubes which are subjected to thelowest temperatures. The control of the quantity of air passing through the different tubes may be effected either by varying the pressure exerted on the different tubes at their inlets or by varying the effective cross-sectional areas of the different tubes. For reasons which should be readily apparent, it is more practical to vary the cross-sectional areas of the tubes.

Other objects and advantages of the invention will be apparent from a' consideration of the following detailed specication and the accompanyingv drawings wherein there is specifically disi closed a preferred embodiment of the invention.

In the drawings:

Figure 1 is a longitudinal sectional view of a furnace constructed in accordance with the principles of the invention; and

Figure 2 is a transverse sectional view of the furnace taken along the line II-H of Figure 1.

In the drawings reference numeral I0 indicates a combustion chamber which may be red either by liquid, solid or gaseous fuel, the particular embodiment illustrated being arranged for liquid fuel firing, the front wall II of the combustion chamber being provided with a plurality of spaced openings I2 to receive the burners. A vertically extending wall structure I3 at the rear of the combustion chamber I separates the combustion chamber from the heating chamberA Il. Below the chamber I4 and preferably extending parallel with the combustion chamber III are the air ducts I5 and I6 which are conveniently incorporated in the concrete foundation for the furnace. As shown in Figure 2, the air ducts I5 and I6 are spaced a substantial distance apart, one being positioned at either end of the heating chamber and are each closed off at the top by means of a perforated plate I1. A plurality of arched air conducting tubes 20, 2| and 22 are carried by the plate I1 with each of the tubes having one of its ends secured in one of the perforations of Vone of the plates I1 and the other of its ends secured in one of the perforations of the other of the plates I1. As evident from Figure 1, the tubes extend upwardly from one of the plates into the heating chamber, thence horizontally through the heating chamber and downwardly into the other of. the said plates. The arrangement of the tubes in the furnace is a nesting one with a series of short tubes connecting the innermost apertures in the plate I1, a series of long tubes' interconnecting the outermost apertures of the plate I1 and intermediate series of tubes interconnecting the intermediate apertures of the plates. In accordance with the present invention the inner or shorter tubes 20 may be of smaller cross-sectional area than that of the outer long tubes 22 with the intermediate tubes of intermediate or progressively larger cross-sectional area. A

Extending horizontally outward from the uppei` portion of the combustion chamber I0 and under the roof 24 of the furnace isa iiue 25 which is bounded on its bottom by a wall 26 made up of a plurality of refractory tiles conveniently supported on the outer series of air conducting tubes 22. 'I'he wall 26 separates the flue 25 from the heating chamber I4 and an opening 21 at the vend of the nue 25 opposite the combustion chamber I0 provides communication between the iiue 25 and the heating chamber. Extending transversely of the heating chamber I4 intermediate the two plates I1 is a vertically disposed baille wall 28, the function of winch is to break up the flow of gases along the iioor of the heating chamber and cause such gases to be diverted upwardly into the vregion of the horizontally extending reaches of the heat transferring tubes 2U-22.

A series of laterally spaced exhaust ports 30 are provided in the end wall of the heating chamber Il opposite the opening 21 to withdraw the products of combustion from the heating chamber. Ports 30 are located near the iioor of the combustion chamber and open into fiues 3| and 32 positioned beneath the combustion chamber through which the gases may pass to a suitable stack or other disposing means.

In operation the products of combustion, mixed with a suitable amount of air coming into the combustion chamber through the opening 33 in the door wall of the furnace, pass from the combustion chamber horizontally outward through the flue 25, downwardly through the opening 21, thence horizontally through the heating chamber Il in wiping contact with the air conducting tube 22and through exhaust ports 30 into the flues 3| and/or 32. By reason of the high temperatures developed in the horizontal flue 25 because of the refractory confining surfaces 24 and 26, complete combustion takes place in the flue, thus insuring high eiiiciency in the combustion of the fuel supply.

Air to be heated may be supplied under pressure to the main duct I5 from whence it iiows upwardly through the tubes 20, 2| and 22 to the main duct I6 from where it may be distributed throughout the area to be heated. By reason of the substantial horizontal width and area of the ducts I5 and I6 the pressure will be substantially equal at the inlets to each of the tubes and will be substantially equal at the outlets of each of the tubes. Greater resistance to ilow will be encountered in the outer tubes 22 because of the greater length thereof but since the outer tubes are of relatively large cross-sectional area a large volume of air will pass through each of such tubes in a given length of time. The diameters of these tubes are so chosen in relation to their q length, the pressure diiierential under which they operate and the temperatures encountered in the heating chamber adjacent the refractory wall 26, that a sufficient volume of flow therethrough to keepthe tubes down to safe temperatures, while insuring anefficient temperature gradient between the infiowing and outflowing air, is effected. Less total friction would normally be encountered in the inner tubes-20 because of their substantially shorter length but, by making these tubes of smaller cross-sectional area, the rate of iiow of the air through the tubes can be reduced thereby maintaining particular volumes of air in the tubes for a longer length of time to impart more heat to the air to insure its attaining a certain desired temperature before it leaves the tube. By decreasing the velocity of the flow of air in the tubes normally subjected to a lower temperature, the recuperative eiect of the furnace -is improved and consequently the overall of eiliciency of the furnace is increased. The metal of all the tubes is also maintained at substantially the same temperature, thereby preventing objectionable variations in expansion and premature failure of certain of the tubes. Also, since the air discharged from each of the tubesV into the exhaust duct I6 is substantially at the same temperature, air stratification within the duct I6 is eliminated, and this is of material advantage in large installations where such ducts are of large size and are divided into horizontal branches as they leave the furnace.

The above specifically described embodiment of the invention should be considered as illustrative only as obviously many changes may be made therein without departing from the spirit or scope of the invention. For example, instead of firing a furnace from an end the same may be center red by positioning the combustion chamber within the arch of the tubes, in which l case the products of combustion pass upwardly and outwardly about the tubes and are exhausted from the furnace along theouter lower ends of the outer tubes. In this rearrangement of the furnace obviously the shorter inner tubes, being closest to the combustion chamber,.will be sub- 'ected to the highest temperatures and would therefore probably be of largercrossfsectional l area than the outer longer tubes, the latter then, being in a region of lower temperature, should pass air at a slower velocity to insure the air reaching desirable temperature before it leaves the tubes and to improve the recuperative operation of the furnace.

said casing to define What Iclaim is:

1. An air heating furnace comprising in com bination a refractory lined casing having a transversely extending wall dening a combustion chamber positioned in the fore part of said casing, a pair of longitudinally spaced air ducts extending transversely below the rear part of said casing, a perforated plate closing oi the top of each of said ducts, a plurality of series of arched air conducting tubes spanning said plates and having their ends communicatingwith the apertures. in said plates, said tubes being positioned in said casing on the opposite side of said wall from said combustion chamber and lying in vertical planes extending longitudinally f of said casing, said series of tubes being arranged in vested relation with the outer and longer of said tubes being of greater cross-sectional area than that of the inner and shorter of said tubes, a refractory baille wall supported immediately above the outerof said tubes and extending from adjacent the upper end of said first mentioned wall to substantially the ,rear wall of a horizontally extending flue' for the products of combustion, and a plurality of exhaust ports for said products of combustion positioned adjacent the forward end of said tubes.

2. An air heating furnace comprising in comtransversely extending bination a refractory wall Vdefining a combustion chamber positioned in the fore part o said casing, a pair of longitdinally spaced air ducts extending transversely below the rear Ipart of said casing, a header plate closing off the top of each of said ducts, a pluralityof series of arched air conducting tubes supported on said plates and having communication therethrough with said ducts, said tubes being positioned inl said casing o'n the opposite sidefof said wall from said combustion chamber and lying in vertical planes extending longitudinally of said casing.

said series of tubes being arranged in nested relation with the outer and longer of said tubes being of greater cross-sectional area than that. l

lined casing having a from adjacent the up 

